1. Field of the Invention
This invention relates to plasma (ionized gas) character displays and particularly to a plasma display employing a multisegment matrix operable in the time division multiplexed (TDM) mode to reduce the number of energizing leads required.
2. Description of Prior Art
Heretofore gas plasma displays, such as used on electronic calculators and electronic digital watches, comprised an enclosure containing an ionizable gas with front and rear electrodes mounted on opposite faces of the enclosure for selectively ionizing the gas between energized opposing electrodes. The electrodes can be in direct contact with the gas, in which case the electrodes can be energized with a direct current voltage, or the electrodes can be insulated from, yet capacitively coupled to, the gas, in which case an alternating current energizing voltage is required. AC-type insulated-electrode plasma displays are currently sold by the National Electronics Division of Varian Associates, Geneva, IL, under the trademark Plasmac and are described in New Electronics, Sept. 17, 1974, pp. 82-87, and Electronics, Nov. 18, 1973, and Jan. 10, 1974, pp. 123-128.
Both types of plasma displays suffer from the disadvantage that individual leads must be connected to the respective electrodes which represent respective elements or bars of the matrix on one side of the panel, together with a lead to a common electrode on the other side of the panel. In a single character display for displaying a numeral and utilizing the familiar seven-segment "matrix 8", seven leads are required for the respective elements of the matrix and one lead is required for the common electrode on the other side of the display, for a total of eight leads. While this requirement is not onerous, when multiple characters must be displayed, the number of requisite leads and their connections to the panel presents a redoubtable problem. For example, in an eight-digit panel, 57 external leads to drive the panel are required: seven leads to each character station (8 .times. 7 = 56), plus one lead for the common front electrode. Thus, 57 conductive pathways must be provided on the panel itself, and 57 mechanical and electronic connections must be made to the panel for these leads. This is a serious disadvantage and leads to problems of increased cost, poor reliability, etc., as will be recognized by those skilled in the art.
In accordance with the present invention, the number of leads required for an eight-digit panel can be reduced by over 50% i.e., from 57 to 27 leads. Even greater percentage reductions in number of leads can be effected for panels with more than eight digits. The reduction in number of connections to the panel, as well as the reduction in the number of leads on the panel itself and concomitant reduction in crowding is quite desirable. The above and other advantages of the invention will become apparent from a consideration of the ensuing description thereof.